I was successful in growing a multi grafted Nuclem and satsumas (Early St Anne, Owari) on a south facing wall of my house for many years up here in the 7b/8a border of Virginia Beach. Initially I did protect the tree until it got too big to protect. At its largest the tree was about 12 ft tall and about 10 ft wide or so. It produced a tremendous amount of the most delicious fruit and we loved it having it while it lasted. Then comes a 20 year freeze that gets down to the single digits for many hours and wipes it out and a large portion of my other inground citrus. Maybe I could have done something to protect it but the size of the tree made it very difficult. I grafted it up pretty high on trifoliate which helped it survive for as long as it did. The rootstock did survive and grew out the next year a little. I planned on regrafting onto it then we had a couple more hard winters that eventually sent it to the grave. If you plan on planting a Xie Shan out you might get a few years out of it and a good number of fruit from it as well. When it gets too big to protect it is likely to get wiped out like mine. Just consider it a very risky perennial and enjoy it while it lasts and replant when it freezes out.
I had a Juanita tangerine that did well for a few years too but eventually froze out in the lower teens. I wouldn't rank it much hardier than satsuma. I believe its location at Juanita's house was the key in getting that one to survive.
I still do have a good number of citrus out in the yard that survived but are still rebounding from taking big hits. I would consider these bulletproof for my area. Most all of my trees are grafted but the ones on their own roots that have made it back are a single changsha, yuzu and a thomasville citrangequat. My grafted Keraji trees which I consider a very good tasting fruit are trying to make their way back too. Other survivors are Glen Citrangedin, Mt Olive Dunstan, Ventura lemandarin, Dimicelli Clem yuz 2-2, Taitri, Ichang lemon, and a few others.
Tracing back to your avocado plans I have had an avocado planted out in my yard for something like 5 years now and it has survived our lowest single digit lows. I did protect it with a comforter and put a light bulb next to it when we got that low. Now it is about 6ft tall and flowering again. I need to mention that it is in a protected area next to my house and greenhouse. It is a cutting grown tree from the large surviving avocado tree in downtown Charleston, SC. Next to it I previously had Joey, Pancho, and about 3 or 4 other 'hardy' avocados that all eventually died off.
I have Artic Frost, Bumper and Orange Frost changsats but have not fully tested them out yet. Small grafts I placed on my inground trees seem to be fairing well. I've been meaning to plant the pottted trees out in the yard since they are on their own roots and would likely come back after a freeze l like my changsha. When they fruited I thought they were all pretty tart but maybe I should've waited a little longer before I sampled them.